"The Internet is one of the most transformative technologies of our lifetimes. But for 2 out of every 3 people on earth, a fast, affordable Internet connection is still out of reach. And this is far from being a solved problem. There are many terrestrial challenges to Internet connectivity - jungles, archipelagos, mountains. There are also major cost challenges. Right now, for example, in most of the countries in the southern hemisphere, the cost of an Internet connection is more than a month's income. Solving these problems isn't simply a question of time: it requires looking at the problem of access from new angles. So today we're unveiling our latest moonshot from Google[x]: balloon-powered Internet access." Insane.

I can't see this working.
Air space violation -> kaboom, bye bye internets.

Altitudes above 12mi (18km) are generally considered to be international airspace.

It is almost impossible to shoot down a high altitude balloon. Very few countries have suitable high altitude missiles. A missile that hits an unpressurised helium balloon will simply punch a small hole in the cover causing a very slow leak.

Using anti-aircraft missiles on baloons? I don't think anyone would be insane enough given the cost of those. Also (correct me if i'm wrong) most anti-aircraft missiles have some kind of proximity fuse so it wouldn't just punch a hole.

Depending on what fighters a country has it might be possible to send those up and gun the things down.